The human role in extinction of species and degradation of ecosystems is well documented. Since European settlement in North America, and especially after the beginning of the Industrial Revolution, we have witnessed a substantial decline in biological diversity of native taxa and profound changes in assemblages of the remaining species. We have ripped minerals from the Earth, often bringing down mountains in the process; we have harvested nearly all the old-growth timber on the continent, replacing thousand-year-old trees with neatly ordered plantations of small trees; we have hunted species to the point of extinction; we have driven livestock across every almost acre of the continent, baring hillsides and facilitating massive erosion; we have plowed large landscapes, transforming fertile soil into sterile, lifeless dirt; we have burned ecosystems and, perhaps more importantly, we have extinguished naturally occurring fires; we have paved thousands of acres to facilitate our movement and, in the process, have disrupted the movements of thousands of species; we have spewed pollution and dumped garbage, thereby dirtying our air, fouling our water, and contributing greatly to the warming of the planet. We have, to the maximum possible extent allowed by our intellect and never-ending desire, consumed the planet. In the wake of these endless insults to our only home, perhaps the greatest surprise is that so many native species have persisted, thus allowing our continued enjoyment and exploitation.

Although insults by Homo sapiens since the Industrial Revolution are well documented and widely acknowledged, abundant archaeological evidence indicates similar actions in the more distant past have led to the rise and fall of 23 major civilizations. Humans clearly have impacted their environments since initially appearing on the evolutionary stage, and human impacts have grown profoundly since the development of agriculture and subsequent technologies (as reviewed by Charles Redman’s 1999 text, Human Impact on Ancient Environments and, in more accessible prose, by Jared Diamond’s 2005 book, Collapse). Concomitantly, the environment has influenced the development of humans and their societies. The interaction between humans and their environments and the relative roles of culture and resources on human societies have received considerable attention from archaeological scholars. (The word “resources” is problematic because it implies materials are placed on this planet for the use of humans. We see finite substances and the living planet as materials to be exploited for our comfort. For efficiency and familiarity, I reluctantly use the word throughout this essay. I’ll save the full rant for another post while pointing out that my perspective is less imperial, and less Christian, than the traditional view.) The expansive literatures on resources, culture, and human-environment interactions indicate the important role of resources in constraining the development of several societies in the North American Southwest (as described particularly well by Timothy A. Kohler and colleagues). Exploitation of ecosystems, even to the point of destroying fertility of soils, has constrained subsequent food production (as described most notably by J.A. Sandor and colleagues). Although I recognize the importance of these topics, I leave the continued study and discussion of culture, resources, and human-environment interactions in the distant past to scholars with more interest and expertise than me, and instead turn my attention to recent and ongoing assaults by humans on the living planet.

If we accept that humans played a pivotal role in loss of species and degradation of ecosystems -- and both patterns seem impossible to deny at this point -- we face a daunting moral question: How do we reverse these trends?

Maintenance of biological diversity is important to our own species because present and future generations of humans depend on a rich diversity of life to maintain survival of individuals and, ultimately, persistence of our species. In addition, as architects of the extinction crisis currently facing plant Earth, we have a responsibility to future Homo sapiens and to non-human species to retain the maximum possible biological diversity. We must embrace our capacity and capability to sustain and enhance the diversity and complexity of our landscapes. The substantial economic cost of maintaining high levels of biological diversity will pale in comparison to the costs of failing to do so, which potentially include the extinction of humans from Earth.

Reintroducing ecological processes with which species evolved, and eliminating processes detrimental to native species, underlie the ability to maintain and perhaps even restore species diversity. Specifically, the management of wildland ecosystems should be based on maintenance and restoration of ecological processes, rather than on structural components such as species composition or maintenance of habitat for high-profile rare species. In fact, a focus on the latter goals -- a fine-filter approach -- may clog the coarse filter necessary for landscape-scale management of many species and ecosystems.

Drivers of Change

The proximate drivers underlying changes in land cover during the first few decades after European contact were mineral extraction, agricultural expansion, timber removal, and introduction of nonnative species (most importantly, livestock). The quest for silver and gold drove the Conquistadors to dismember, rape, and murder native peoples throughout the New World. The effects of mining on natural ecosystems were no less dramatic. Even before fossil fuels were employed to ease the extraction of metals from the ground, waterways were diverted and steam-powered water cannons were used to blast soil from mountains. Every tree within several dozen miles of a mining operation was cut down or pulled from the ground to power steam-powered stamp mills. Trees that escaped the eye of mine operators rarely got away for long. The western expansion of the human population across North America drove great demand for construction lumber, railroad ties, paper products, and heat from the hearth. These changes and their consequences have been well documented in a wide variety of publications (see, for example, People’s History of the United States by Howard Zinn, One with Ninevah by Paul Ehrlich and Anne Ehrlich, and The Diversity of Life by Edward O. Wilson,).

Farmers and ranchers followed frontiersmen, trappers, and miners into western North America. Whereas frontiersmen left a relatively small ecological footprint and the operations of trappers and miners tended to be limited in spatial scale, agriculture dominated virtually every acre of the North American West. Row-crop agriculture covered areas with fertile soil that could be fed by irrigation systems, including nearly all rivers. The massive, arid expanses unable to sustain row crops supported the dominant form of agriculture: livestock. By the early twentieth century, cattle and sheep had trampled nearly every wildland acre in search of forage. Stockmen (and, rarely, stockwomen) led the charge to exterminate perceived predators and potential competitors for forage: wolves, bears, coyotes, eagles, and prairie dogs were among the species slaughtered in the pursuit of safe environs for livestock and those who grew them. Perhaps more important than direct mortality from shooting and trapping were pronounced changes in site conditions that resulted from the collective action of millions of mouths and hooves.

Livestock have had pronounced negative impacts throughout North America. Livestock still loom large, and other biological invasions have transformed western landscapes. Some, like livestock, are politically “untouchable” despite adverse impacts on native species and ecosystems (e.g., “sport” fishes and various species of turf grasses critical to the golf-course industry). Others are universally undesirable but seemingly intractable because of ecological, rather than political, reasons.

It is not surprising that we are largely unable to manage, much less eradicate, nonnative species. After all, there are more than 50,000 nonnative species in the United States alone, invading terrestrial ecosystems at the rate of 700,000 hectares each year at an annual cost of $120 billion; they threaten 400 species with extinction (these figures come from the excellent scholarship of David Pimentel and colleagues, most notably including their 2005 paper in the journal Ecological Economics titled, “Update on the environmental and economic costs associated with alien-invasive species in the United States”). To make matters even more challenging, every species on Earth is capable of invading other sites (as assured by biotic potential), and every site is subject to invasion by at least one, and potentially many, nonnative species. Because biological invasions depend exclusively on the “match” between characteristics of biological invaders and characteristics of sites, and because there are an infinite number of potential “matches” between species and sites, solutions to the problem of biological invasions are specific to species and sites.

Given the disinterest in environmental issues displayed by citizens and their elected representatives, I doubt we will seriously address the problem of biological invasions before we cause the extinction of own species. As such, this disinterest in environmental issues reflects ignorance or disdain for the living planet that sustains our own species. It represents, in other words, omnicide that will almost certainly prove fatal.

The transition to modernity brought infrastructure, notably cities and the ever-widening, increasingly well maintained roads between them. Thus, within the last few decades, early drivers of change such as mining and agricultural expansion have been supplanted in importance by alteration of fire regimes, urbanization, and global climate change. Herein, I focus on the relatively simple impacts of each of these factors in isolation. As with historical drivers of change, interactions between these factors are complex, under-studied, and undoubtedly critically important.

A large and growing body of knowledge and empirical evidence indicates that fire was historically prevalent in North America, except in the driest deserts and the coldest tundra. It is clear that native species on the continent have evolved adaptations to periodic fires. Historical prevalence of fire ensures that even those species that seem most intolerant of fire have evolved in the presence of recurrent fires, as described in abundant ecological literature. Adaptations to fire are many and diverse, and include escape (e.g., distributions limited to rocky areas where fire rarely occurred), tolerance (e.g., thick bark), and rapid recruitment in post-fire environments (e.g., widely dispersed seeds and ability to establish in open environments).

Recognition that virtually all native species in North America evolved in concert with periodic fires leads to two general conclusions: (1) Native species have developed adaptations to fires that occur at a particular frequency, season, and extent; and (2) maintenance or reintroduction of the fire regimes with which these species evolved should assume high priority for those interested in maintaining high levels of biological diversity. A corollary to the first conclusion is that classification of native species along a gradient of adaptation to fire is simplistic and potentially misleading. Native species are “adapted” to recurrent fires, and classifying some as more tolerant than others suggests that fire is “good” for some species and “bad” for others. A more appropriate view is that recurrent fires, at the appropriate frequency, season, and extent (i.e., components of the historical fire regime), are part and parcel of these ecosystems. A corollary of the second conclusion is that reintroduction of ecological processes should be a relatively efficient and comprehensive strategy for retaining native species in extant ecosystems. Indeed, the historical prevalence of fire in these ecosystems suggests that fire is a necessary component of any comprehensive strategy focused on retention of biological diversity. Because fire was -- and is -- a dominant process in these systems, restoration of fire regimes would seem to be an important first step toward maintenance of high levels of biological diversity.

Urbanization and the associated transportation infrastructure have divided formerly large, contiguous landscapes into fragmented pieces. Fires that formerly covered large areas are constrained by fragmentation, and animals that necessarily range over large areas, such as mountain lions, bison, and grizzly bears, have suffered expectedly. These changes have been particularly pronounced since Oil War II, largely as a result of government subsidies that have promoted growth of the human population and suburban development. These trends will be reversed within the next few years because the Oil Age is drawing to a close. Unfortunately, our near-term inability to burn fossil fuels on a large scale probably will come too late to save many of the planet’s species from the effects of runaway greenhouse.

Ultimately, the story of western civilization is the story of fossil fuels. Profound changes in land use and land cover have been enabled by access to inexpensive oil and its derivatives (e.g., coal, uranium, ethanol, photovoltaic solar panels, wind turbines). Dramatic fluctuations in the price of oil within the next few years, coupled with steadily declining global supplies of this finite substance, likely will cause a complete collapse of the world’s industrial economy, which might usher in a new era with respect to species assemblages and land cover. Given the dependence of humans on fossil fuels for power, water, and food (including production and delivery), it seems inevitable that many people will die and the industrialized world’s vaunted infrastructure will collapse, thereby giving other species a slim and dwindling chance to make a comeback. Although the pattern of dwindling access to resources and subsequent collapse of civilizations has been thoroughly described in the archaeological record, the ongoing collapse obviously exceeds previous others with respect to geographic scale, as well as the number of species and the number of humans impacted.

Peak Oil and the Collapse of Industrial Civilization

Oil discovery and extraction tend to follow bell-shaped curves, as described by M. King Hubbert more than 50 years ago. The easily reached, light oil is extracted first. Heavier oil, often characterized by high sulfur content, is found at greater depths on land and also offshore. This heavier oil requires more money and more energy to extract and to refine than light oil. Eventually, all fields and regions become unviable economically and energetically. When extracting a barrel of oil requires more energy than contained in the barrel of oil, extraction is pointless.

The top of the bell-shaped curve for oil extraction is called “Peak Oil” or “Hubbert’s Peak.” We passed Hubbert’s Peak for world oil supply in 2005 and began easing down the other side, with an annual decline rate of 0.5% between 2005 and 2008 leading to a record-setting price of $147.27/barrel in July 2008. The International Energy Agency, which had never previously acknowledged the existence of a peak in oil availability, predicted an annual decline rate in crude oil in excess of 9% after 2008. The current economic recession resulting from the high price of oil led to a collapse in demand for oil and numerous other finite commodities, hence leading to reduced prices and the rapid abandonment of energy-production projects. Many geologists and scientists predict a permanent economic depression will result from declining availability of oil and the associated dramatic swings in the price of oil. It seems clear the permanent depression is already here. The absence of a politically viable solution to energy decline explains, at least in part, the absence of a governmental response to the issue even though the United States government recognizes peak oil as a serious problem (along, no doubt, with many other governments of the world).

Without energy, societies collapse. In contemporary, industrialized societies, virtually all energy sources are derived from oil. Even “renewable” energy sources such as hydropower, wind turbines, and solar panels require an enormous amount of oil for construction, maintenance, and repair. Extraction and delivery of coal, natural gas, and uranium similarly are oil-intensive endeavors. Thus, the decline of inexpensive oil spells economic disaster for industrialized countries. Demand destruction caused by high energy prices is affecting the entire industrialized world.

Viewed from a broader perspective than energy, economic collapses result from an imbalance between demand and supply of one or more resources (as explained in considerable depth by Jared Diamond in Collapse). When supply of vital resources is outstripped by demand, governments often print currency, which leads to hyperinflation. In recent history, the price of oil and its refined products have been primary to rates of inflation and have played central roles in the maintenance of civilized societies.

Addressing the issue of peak oil while also controlling emissions of carbon dioxide, and therefore reducing the prospect of “runaway greenhouse” on planet Earth, represents a daunting and potentially overwhelming challenge. Peak oil and the effects of runaway greenhouse are the greatest challenges humanity has ever faced. Tackling either challenge, without the loss of a huge number of human lives, will require tremendous courage, compassion, and creativity.

There is little question that the decades ahead will differ markedly from the recent past. From this point forward, Homo sapiens will lack the supply of inexpensive energy necessary to create and maintain a large, durable civilization. The fate of western civilization is in serious question, given our inability to sustain high levels of energy extraction. The population of humans in industrialized countries probably will fall precipitously if oil extraction turns sharply downward, as predicted by the International Energy Agency. The benefit of a massive human die-off is the potential for other species, and even other cultures, to expand into the vacuum we leave in our wake. ________

This post is extracted and modified from a forthcoming book chapter celebrating 20 years of archaeological research in the North American Southwest. To improve accessibility for this audience, I have removed references to the primary literature (if you’d like a copy of the academic version, please send me an email message). The book will be published by the Colorado University Press. Thanks to Carla Van West for inviting my participation in the Southwestern Symposium held in Tempe, Arizona, January 2008, and for soliciting my chapter for the book. Thoughtful comments on earlier drafts were provided by Dana Backer and Paul Taylor.

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